User blog comment:DarkSlayer 3/Theories/@comment-11242027-20130624233537/@comment-5621513-20130626135932

I know it seems impossible for Vergil to sleep with a human due to his disdain for them but what if he thought that Nero's mother wasn't human? He could've assumed she was a deamon (or other species, just not human) and seduced her in order to gain more power. So, when he finds out she's human he basically leaves her to rot and then goes to Temen-ni-gru.